<template>
    <ul class="alphabet">
        <li 
            class="item"
            v-for="item in letters" 
            :key="item" 
            @click="handleLetterClick"
            @touchstart = "handleTouchStart"
            @touchmove = "handleTouchMove"
            @touchend = "handleTouchEnd"
            :ref="item"
        >
            {{item}}</li>
    </ul>
</template>
<script>
export default {
    name:'Alphabet',
    props:{
        cities:{
            type:Object,
            default(){
                return {}
            }
        }
    },
    computed:{
        letters(){
            const letters = []
            for (const key in this.cities) {
                letters.push(key)
            }
            return letters
        }
    },
    created(){
        this.touchStatus = false
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                const startY = this.$refs['A'][0].offsetTop
                const touchY = e.touches[0].clientY-79
                const index = Math.floor((touchY-startY)/20)
                if(index>=0 && index<this.letters.length){
                    this.$emit('change',this.letters[index])
                }
                
            }
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    }
}
</script>
<style lang="stylus" scoped>
@import '../assets/styles/varibles.styl'
.alphabet
  position absolute 
  display flex
  justify-content center
  flex-direction column
  top 1.58rem
  right 0 
  bottom 0
  width .4rem
  .item 
    line-height .4rem
    text-align center 
    color $bgColor
</style>